Enabling Code Sonic
To enable Code Sonic, you simply need to name your character "Code Sonic" when you create it. This will enable an option in the in-game menu called Super Speed, which greatly increases the player's sprinting speed and changes the sprint animation to a Sonic-like roll.
Code Sonic was part of a secret Puzzle which occurred in February 2019, before the official release of the game. Original it only worked on PC, but as of the October 2019 Patch it works on all platforms. See this page for more details on the puzzle.